A fluororesin film can maintain weather resistance, transparency, stain resistance, etc. for a long period of time, and therefore such a film is applied to e.g. agricultural house films or outdoor building materials (such as roof materials).
The fluororesin film to be used for the application is required to have ultraviolet shielding properties from the following reasons:
(i) In a case where the fluororesin film is bonded to a base material via an adhesive to be used as an outdoor stuffs, the adhesive is deteriorated by ultraviolet light.
(ii) In a case where the fluororesin film is applied to agricultural house films, it is necessary to adjust the amount of ultraviolet light so as to improve e.g. colors, Brix or crop yields of plants to be cultivated. Further, in order to suppress activities of harmful insects in the agricultural house, it is necessary to shield the ultraviolet light.
As a fluororesin film having ultraviolet shielding properties, the following fluororesin film has been proposed.
(1) A fluororesin film containing titanium oxide particles or zinc oxide particles (Patent Document 1). However, the fluororesin film as the above (1) has the following problems:
(i) The dispersibility of titanium oxide particles or zinc oxide particles in a fluororesin is poor, and such particles are agglomerated and a fluororesin film is thus whitened, whereby transparency is deteriorated.
(ii) The fluororesin film is deteriorated by photocatalysis of the titanium oxide particles.
(iii) Zinc oxide particles are reacted with fluorinated compounds liberated from a fluororesin at the time of producing a fluororesin film or using it outside, whereby they are formed into zinc fluoride, and therefore the ultraviolet shielding properties are weakened.
As a fluororesin film having durability to fluorinated compounds and further containing zinc oxide particles having their dispersibility in the fluororesin improved, the following fluororesin film has been proposed.
(2) An amorphous silica-coated fluororesin film containing zinc oxide particles, wherein the amorphous silica is hydrophobized with ethyltriethoxysilane (Patent Document 2).
However, the fluororesin film as the above (2) is required to be further improved from the following points:
(i) Since such hydrophobized amorphous silica-coated zinc oxide particles are easily agglomerated, the dispersibility in a fluororesin is likely to be insufficient, whereby the transparency of the fluororesin film tends to be deteriorated.
(ii) Since a pulverizing step is needed at the time of producing hydrophobized amorphous silica-coated zinc oxide particles, the zinc oxide particles are likely to be insufficiently coated with amorphous silica, whereby the resistance to fluorinated compounds tends to be insufficient.
Patent Document 1: JP-A-7-003047
Patent Document 2: JP-A-11-279358